Recently, various types of digital appliances (such as optical disk recorders and camcorders) that can write and store digital data, representing a content, on a number of types of media including an optical disk such as a DVD, a magnetic disk such as a hard disk, and a semiconductor memory, have become more and more popular. The content may be a broadcast program or the video and audio that have been captured with a camcorder, for example.
Also, PCs often have the functions of recording, playing and editing a content lately, and may also be regarded as being included in those digital appliances. In writing data such as document data, PCs have used various media such as a hard disk, an optical disk and a semiconductor memory. That is why a file system that has a data management structure compatible with a PC such as a file allocation table (FAT) has been adopted in such media. The FAT 32 system that is often adopted currently can handle a file that may have a maximum size of 4 gigabytes or can manage a medium with a maximum storage capacity of 2 terabytes.
The bigger the maximum storage capacity of a medium, the longer the overall content recording duration. The optical disks, hard disks, semiconductor memories and so on are so-called “randomly accessible” media. Therefore, when a data stream representing a content with a long duration is stored on such a medium, it would be convenient if playback could be started from any arbitrary location of the content.
For example, Patent Document No. 1 identified below generates time map information, defining correspondence between a playback time and the address at which the AV data to play back at the time is stored, at regular time intervals from the beginning of a data stream. If the start time and end time, specified by the user, are converted into a start address and an end address, respectively, by reference to the time map information and if the data stored at those addresses are read, the content can start being played back at the specified time.
Meanwhile, a lot of storage media, in which the FAT file system has been established, are currently available for sale. For instance, a removable semiconductor memory (i.e., a memory card) usually has its file management done by an FAT file system.
In a semiconductor memory, the target recording address is specified on the basis of a data unit of 512 bytes, which is called a “sector”. A logical address is allocated to each address on a sector-by-sector basis.
In an FAT file system on the other hand, the availability and non-availability of the storage areas are managed on the basis of a unit called “cluster”. For example, if the semiconductor memory has a storage capacity of 2 gigabytes or less, then one cluster has a data size of 32 sectors (i.e., 16 kilobytes). In that case, a file system called “FAT 16” is used. However, if the semiconductor memory has a storage capacity exceeding 2 gigabytes, then one cluster has a data size of 64 sectors (i.e., 32 kilobytes). In that case, a file system called “FAT 32” is used.
In recording a data stream on such a semiconductor memory, the writing rate varies with the degree of continuity between the sectors to be written. For example, if the sectors to be written had non-serial numbers, then the writing rate would decrease. This is because if a written sector and a sector to be written were included in the same cluster, then the written data should be read once and rewritten and then new data should be written, thus causing a processing delay.
Stated otherwise, if writing is done continuously on a number of consecutive sectors or clusters, then data can be written at a higher rate than an ordinary writing rate that is supposed to be adopted in normal applications.                Patent Document No. 1: Japanese Patent Application Laid-Open Publication No. 11-155130        